1. Field of the Invention
The present invention relates to a resonator device including a plurality of resonators, a filter, a duplexer, and a communication apparatus using the resonator device.
2. Description of the Related Art
Publicly known resonators capable of handling a relatively large amount of power in a microwave band include cavity resonators and semi-coaxial resonators. A semi-coaxial resonator is also referred to as a coaxial cavity resonator. It has a relatively high Q factor, and is smaller than a cavity resonator. Accordingly, the use of semi-coaxial resonators contributes to the miniaturization of filters and the like.
However, for example, in a cellular mobile communication system such as a mobile phone system, with the spread of micro-cellular networks, there has been a growing demand for more compact filters for use in base stations.
On the other hand, when the number of stages of resonators is increased in a filter using a semi-coaxial resonator, a number of additional resonators equivalent to the number of increased stages are needed, with the result that the entire filter becomes larger.
Accordingly, the present invention provides a multi-mode resonator device, which can be miniaturized even while increasing the number of resonators, using either a semi-coaxial resonator or a coaxial resonator. Coupling between a TEM mode of the semi-coaxial resonator and another resonance mode such as a TM mode can be facilitated, so that coupling can be provided between the resonators with a predetermined coupling strength.
The present invention also provides a filter, a duplexer, and a communication apparatus using the resonator device.
According to a first aspect of the present invention, there is provided a resonator device including a conductive cavity, a conductive rod disposed in the cavity, at least one end of the conductive rod being conductively connected to the inside of the cavity, a dielectric core disposed in the cavity, the resonant frequency of a quasi-TEM mode generated by the conductive rod and the cavity being substantially equalized with the resonant frequency of a quasi-TM mode generated by the dielectric core and the cavity, and a conductive member disposed such that it is disposed at or removed from a place where the magnetic field of one of two coupling modes generated by the quasi-TEM mode and the quasi-TM mode is strong and the magnetic field of the other coupling mode is weak.
In addition, according to a second aspect of the present invention, a resonator device includes a dielectric member and a conductive member disposed such that they are disposed at or removed from a place where the electric field of one of two coupling modes generated by the quasi-TEM mode and the quasi-TM mode is strong and the electric field of the other coupling mode is weak.
These structures make a difference between the resonant frequencies of the two coupling modes obtained from the quasi-TEM mode and the quasi-TM mode to enable the coupling between the quasi-TEM mode and the quasi-TM mode.
Furthermore, according to a third aspect of the present invention, a resonator device includes a conductive cavity, a conductive rod disposed in the cavity, at least one end of the conductive rod being conductively connected to the inside of the cavity, a dielectric core disposed in the cavity, the resonant frequency of a quasi-TEM mode generated by the cavity and the conductive rod being substantially equalized with the resonant frequency of a quasi-TM mode generated by the cavity and the dielectric core, and a dielectric member and a conductive member disposed such that they are disposed at or removed from a place where the electric-field vectors of the quasi-TEM mode and the quasi-TM mode significantly overlap each other.
In addition, according to a fourth aspect of the present invention, a resonator device includes a conductive member and a magnetic member disposed such that they are disposed at or removed from a place where the magnetic-field vectors of the quasi-TEM mode and the quasi-TM mode significantly overlap each other.
With the structure, the quasi-TEM mode and the quasi-TM mode are coupled with each other.
Furthermore, in this invention, the resonator device may further include a hole formed substantially at the center of the dielectric core with the conductive rod passing through the hole, and the conductive rod may be arranged in such a manner that the center of the conductive rod is shifted from the center of the hole, instead of disposing or removing the conductive member.
Furthermore, the resonator device of the invention may further include a hole formed in the dielectric core with the conductive rod passing through the hole in such a manner that the center of the hole is shifted from the center of the conductive rod, instead of disposing or removing the dielectric member.
As a result, by arranging the conductive rod or the hole through which the conductive rod penetrates, the quasi-TEM mode and the quasi-TM mode are coupled with each other.
Furthermore, in the resonator device of the present invention, the quasi-TM mode may include dual quasi-TM modes having electric fields directed perpendicularly to the dielectric core. With this structure, the resonator device resultantly includes a triplex-mode resonator using the dual quasi-TM modes and the quasi-TEM mode.
In the resonator device of the present invention, the conductive member may be disposed on an inner surface of the cavity at a position overlapping with the dielectric core when viewed from the axial direction of the conductive rod. As a consequence, bonding and arrangement of a coupling conductor member can be simplified and therefore the device can be easily manufactured.
In addition, in the resonator device of the present invention, the conductive member may be integrally molded with the cavity. As a consequence, the resonator device can be manufactured easily.
In addition, in the resonator device of the invention, the conductive member may be a metal screw arranged on the conductive cavity in such a way that the amount of insertion into the cavity can be changed from the outside. In this arrangement, the conductive member can be used for coupling adjustment by a simple turning operation.
According to a fifth aspect of the present invention, a filter includes the resonator device of the invention, and input and output conductors for inputting and outputting signals by coupling with predetermined resonance modes of the resonance modes.
According to a sixth aspect of the present invention, a duplexer includes a pair of filters formed by the above filter. In this duplexer, an input port of a first filter is a transmission signal input port, an output port of a second filter is a reception signal output port, and an input and output port common to the first and second filters is an antenna port.
According to a seventh aspect of the present invention, a communication apparatus includes one of the filter and the duplexer described above.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings.